The present invention relates to a time synchronization transmitter-receiver system to be used between a master station and a remote station in any system in which the actual time of events needs to be known. An example of an application of this invention would be in the electric utility industry where various remote stations record electric meter readings on various branches and the actual time of the meter reading must be recorded. The present invention provides for a master station, such as the electric utility headquarters, to periodically update various substations with the actual time of day reading so that the remote station clock will accurately record the time of day of electric meter readings.
The need for this periodic time of day updating is necessitated by such things as power outages or brief power interruptions which may delay time clock data or perhaps destroy time clock data altogether. The necessity of recording the actual time of day together with electric meter readings is caused by the practice of electric utilities to bill electricity at different rates depending upon time of day usage. This is related to the well-known fact that electricity generated at peak electric demand times tends to be higher cost because of less efficient generating plants and higher cost fuels used in such plants. Obviously, this invention would have application to any use involving various remote stations which must have a local clock having accurate time of day information.
The prior art related to the recording of events at remote stations tends to deal more with the synchronization of events at a remote station to a master station than to the provision of an accurately synchronized actual time of day signal for a remote station clock. For example, U.S. Pat. No. 4,114,141 shows the use of UP-counters in a central station to accumulate information in synchronization with DOWN-counters at remote stations counting to zero. The synchronization is provided by the power line frequency. The mark-space transitions are broadcast as radio timing signals. The term synchronization as used in connection with the patent is related to the coordination of master and remote transmission of information. The present application is related to the synchronization of an actual time of day clock at a remote station with respect to a master clock at a master station.
Also known to applicant in U.S. Pat. No. 3,798,650 which shows the use of a counter actuated upon receipt of a synchronization signal to produce an internal count representing the time interval until the occurrence of an internal reference pulse. This interval count is then used to perform various functions. U.S. Pat. No. 3,142,802 shows a counter means actuated by a remote unit and used internally in a local unit to derive synchronous pulse signals. Again, these patents use the term synchronization in the sense of locking activities in step with one another or causing an activity to be set to an initial state.